NL8100379A - METHOD FOR PREPARING POLYESTERS OF LARGE MOLECULAR WEIGHT - Google Patents

Description

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Process for preparing high molecular weight polyesters.

The invention, as described in more detail below, relates to an improvement in the preparation of high molecular weight linear condensation polyesters by means of solid phase polymerization of corresponding particulate melt-polymerized low molecular weight polyester prepolymer resins. More particularly, the invention relates to a process for the rapid and simultaneous crystallization, drying and heating of these particulate prepolymer resins to solid phase polymerization temperatures by high frequency energy prior to subjecting the prepolymer resins to solid phase polymerization. -circumstances.

Generally, two different main process steps are used in the preparation of high molecular weight polyesters using solid phase polymerization techniques. The first stage involves the preparation of a low molecular weight polyester prepolymer resin using a discontinuous or continuous melt phase polymerization process. The resulting melted prepolymer is then solidified and converted into a particulate form such as, for example, granules, 20 'diced cubes, granules, powders, etc., and is known in the art as a solid phase feed polymer.

This solid phase prepolymer or feed polymer (these terms are used interchangeably in the description) will usually be one. have intrinsic viscosity in the range of from about 0.55 to about 0.60 and a moisture content ranging from about 0.40 to about 0.25 wt. 96 and will be amorphous 3, as shown by its density of 1, 54 per cm or less.

The second stage involves the actual solid phase polymerization of the above-described particulate prepolymer to the desired high molecular weight product. For polyethylene terephthalate, the solid phase polymerization step is usually carried out at temperatures ranging from about 185 ° C to about 250 ° G and preferably from about 220 ° C to about 240 ° C in an inert gas atmosphere 55 or under a reduced pressure using discontinuously operated rotary mixer dryers, fluidized bed dryers, dish dryers or continuously in reaction towers with 81 0 0 37 9 --------- ί> ν ....... j * $ -____________ ____________: -. . . . "· ..I ..

s' 2 gravity flow.

Moreover, it is a well known and accepted fact that due to the moist, amorphous nature of this prepolymer, it is necessary to subject the prepolymer to an intermediate stage, whereby the prepolymer is heated, dried and crystallized to degrade and agglomerate the prepolymer. avoid when exposed to solid phase polymerization conditions. It is also known that when subjecting this moist, amorphous prepolymer to this intermediate stage, the particulate polymer will tend to agglomerate into an unmanageable mass, just as with the solid phase polymerization stage, unless steps are taken to prevent this melting. appearance.

A measure to prevent melting of the particulate prepolymer during heating, drying and crystallization there-15. of, the prepolymer is subject to vigorous motion. Examples of methods for the pretreatment of polyester prepolymer involving vigorous motion. of the prepolymer are described in U.S. Pat. Nos. 4 * 064 * 112 and 4 * 161,578 *. However, a major drawback of processes is that vigorous movement of the particulate prepolymer is employed during heating, drying and crystallization. thereof, the development of fine polymeric components, which may comprise from about 0.06 to about 0.11% by weight of the total weight of the prepolymer to be treated. The presence of these fines in the prepolymer is undesirable, not only because they give rise to handling problems, but also because of the adverse effect they have on the quality and uniformity of the final polymer product and its behavior when subjected to treatment. such as melt spinning and injection molding.

Another approach to the heating, drying, and crystallization of particulate wet amorphous polyester prepolymer prior to its solid phase polymerization is the process described in U.S. Pat. No. 3 * 634 * 359. This patent describes an improvement in a process for the preparation of high molecular weight polyesters, in particular high molecular weight polyethylene terffcalate, by post-condensation of the corresponding low molecular weight polyester in the solid phase. It is explained that the specific improvement in the process is the drying, crystallization and heating of the low molecular weight prepolymer to solid phase polymerization temperatures by high frequency energy in the presence of a flowing dry gas.

In the practice of the method described in the above patent specification, it has been determined that the use of a flowing dry gas and the manner in which the high-frequency heating is carried out are extremely important limitations in the successful implementation of the method. According to this patent, the use of a flowing dry gas is essential for the immediate withdrawal of water released from the polyester during the heating process, when hydrolytic decomposition of the polyester is to be maintained within acceptable limits and the heating is . must be carried out in such a way that the temperature trajectory at which crystallization takes place at optimum speed is not exceeded before the polyester has taken on the crystallite form to avoid melting of the granulated polyester into a solid lump.

The specific manner in which the heating is to be carried out is described as consisting of either slow heating of the polyester to the condensation temperature, ie between 5 and 15 minutes with constant movement of the granulated polyester, the very rapid heating of the polyester to 100 ° C - 180 ° C, maintaining the polyester in a field-free space at the temperature reached until it has crystallized sufficiently and then and only subjecting this crystallized polyester to further heating at high frequency to raise its temperature to condensation temperatures. The adverse effects that occur as a result of not using a flowing dry gas and too rapid heating are illustrated in Example III of the 5Q patent. In that example, granulated polyethylene terephthalate was heated to 240 ° C within 5 minutes and in the absence of a flowing "dry gas. The effects of such rapid heating and the absence of a flowing dry gas were that the material melted together into a solid lump and that the specific viscosity 55 (which is a measure of its molecular weight) of the material was reduced from an original value of 0.88 to a value of 0.75, a reduction of 17%

Applicants have now found that, contrary to the teachings of the aforementioned U.S. Patent Specification, a low molecular weight part-40 polyester prepolymer resin is rapidly 81 0 0 37 9 ....... «........ ~ '........... .....' '4 and can be heated continuously in a high frequency energy field to solid polymerization temperatures of 185 to 250 ° C either in the absence or in the presence of a running dry gas, such as nitrogen or air, to simultaneously achieve the desired crystallization, drying and heating of the prepolymer resin without a significant reduction in its molecular weight or the formation of a solid, non-brittle mass.

Accordingly, the present invention includes an improvement in the preparation of high molecular weight particulate linear condensation polyesters with intrinsic viscosities of at least 0.6 dl per g by solid phase polymerization of corresponding particulate melt-polymerized linear condensation - low molecular weight polyester prepolymer resins with intrinsic viscosities of at least 0.35 dl. per g, which simultaneously and continuously improve (a) crystallization of the particulate prepolymer resin having an initial density of 1.34 g per cm or less to a density range from about 1.57 to about 1.39 g per cm 2, (b) drying the particulate prepolymer resin with an initial water content of about 0.40% to about 0.25% to a water content ranging from about 0 , 10% to about 0.005% and (c) heating this particulate prepolymer resin to a solid phase polymerization temperature hours ranging from about 185 ° C to about 250 ° C, and preferably includes about 210 ° C to about 240 ° C, by subjecting the particulate prepolymer to a continuous and continuous high frequency field ranging from about 20 MHz to about 300 MHz for a time period ranging from about 20 seconds to about 90 seconds. The invention is illustrated more fully with reference to the examples listed below.

The reported intrinsic viscosities for all polyester samples were determined using a solution containing 0.4 g of polymer in 100 ml of a mixed 60/40 phenol / t rachloro thane solvent measured at 30 ° C. All percentages given for it. moisture content of both untreated and treated polyester 55 prepolymer resins are percentages by weight unless otherwise indicated. All tests were performed in the absence of a flowing dry gas.

Example I

A particulate melt-polymerized polyethylene-40. terephthalate prepolymer resin with an intrinsic viscosity of 81 0 0 37 9 5

Z.

0.52 dl / g, a density of 1.54 S per cm and a water content of 0.54% was continuously deposited on a 5 cm wide moving conveyor of a high frequency heating device, which conveyed the resin between two opposite each other vertically.

5 electrodes placed. The resin was continuously and continuously exposed to a high frequency energy field of 27 Mz and heated to 210 ° C as the resin passed through the high frequency device at a rate of 15 hg per hour.

The high energy field exposure time of any given resin particle was about 64 seconds. The crystallized, dried and heated resin exited the high-frequency brittle cake heater which, when subjected to very low pressure, crumbled by hand into individual particles of the same size and configuration as the starting prepolymer. The treated resin had an intrinsic viscosity of 0.51 dl / g, a density of 1.59 g / cm 2 (i.e., a crystallinity of about 50%) and a water content of 0.06%,

Example II

In a similar manner as used in Example 1, a 20 µm, melt-polymerized polyethylene terephthalate prepolymer having an intrinsic viscosity of Q, 59 dl / g and a density of about 1.54 g / cm 2 was continuously added to a 58 cm wide conveyor of a high frequency heating device through which the resin was conveyed between two opposed horizontally positioned electrodes.

The resin was continuously and continuously exposed to a high energy field of 100 MHz as the resin passed through the high frequency heater. As it passed through the high frequency heater, the granulated pre-50 polymer was heated from ambient temperature (about 24 ° C) to about 210 ° C with the residence time of each resin particle in the high energy field about 25 seconds. The crystallized, dried and heated prepolymer resin particles had only very little adhered together when they left the device and were easily broken apart using a very low pressure by hand. The treated resin had an intrinsic viscosity of 0.58 dl / g and a density of about 1.39 g / cm 3 (i.e., a crystallinity of about 31%)

Example III

40 In order to reduce the brittle nature of the particulate melting 81 0 0 37 9 6. - polymerized polyethylene terephthalate prepolymer resin, which has been crystallized, dried and heated to the solid phase condensing temperatures at the same time in a timely manner to further demonstrate the process of the present invention, a small glass beaker was completely filled with particulate prepolymer with an intrinsic viscosity of 0.45 dl / g. The prepolymer-filled beaker was then placed in a high energy field of 27 MHz and heated rapidly and continuously until the prepolymer had reached a temperature of about 205 ° C, as measured by an optical pyro-10 meter. The total exposure time of the prepolymer to the high energy field was 60 seconds. The beaker was then removed from the field and vice versa to remove the prepolymer resin, the particles of which were adhered together, to form a brittle mass in the shape of the beaker. Using very low pressure by hand, the mass was easily and quickly broken back into individual particles. Comparative example

In order to avoid the need for rapid heating (ie between 20 and 90 seconds) when high frequency energy is used to simultaneously crystallize, dry and heat the prepolymer according to the method of the present invention and the need to use a field with high energy of. . To illustrate at least 20 MHz, a particulate polyethylene terephthalate prepolymer resin having an intrinsic viscosity of 0.50 dl / g was placed in a glass dish 55 cm x 25 cm x 6 cm deep. The tray containing the granules was then placed in a high energy field of 16 MHz and heated to 210 ° C. It took 2.5 minutes to reach the desired temperature.

When the heated material was removed from the high energy field and then 50 from the glass dish, it had the form of a solid mass according to the shape of the dish, which could not be broken into individual particles without the use of high pressure.

Example 17 55 About 23.0 kg of polyethylene terephthalate prepolymer resin treated in accordance with Example I was subjected to discontinuous, solid phase polymerization conditions in a rotary mixer / dryer polymerizer. The polymerization was carried out under reduced pressure at about 237 ° C. After a residence time 40 of 9 hours, the intrinsic viscosity of the resin had increased 8100379

Tan 0.51 dl / g to 0.72 dl / g and increased to 0.85 dl / g after a total residence time of 15 * 6 hours.

From the foregoing examples, it is apparent that, contrary to the teachings of U.S. Pat. to a molten, unusable mass and without any substantial adverse effect on the properties of the prepolymer, such as a reduction in its molecular weight as suggested! by the intrinsic viscosity values.

The latter result is particularly surprising in view of the fact that in the previous examples no flowing dry gas was used to remove moisture released from the prepolymer resin subjected to the high frequency energy field *

High frequency energy levels ranging from 20 MHz to 300 MHz can be used in the practice of the invention of the present application. A more preferred range is from about 25 MHz to about 150 MHz, with a range from about 27 MHz to about 100 MHz being most preferred.

The specific level of high-frequency egg used to simultaneously and continuously crystallize, dry and heat the polyester prepolymer resin to solid phase polymerization temperatures of the present invention will depend upon the length of time the prepolymer resin will be exposed to the field with high frequency energy and the initial temperature of the output prepolymer resin. Generally, a higher energy level will be required for short exposure times, for example

i.C.

20 seconds, and a "lower energy level for long exposure times, for example 90 seconds. Torch will require a prepolymer resin with a lower initial temperature, for example room temperature, a higher energy level than a prepolymer with a higher initial temperature, ie a temperature higher than ambient temperature, for e and given exposure time between 20 and 90 seconds.

In actual practice, the starting temperature of the starting prepolymer can range from ambient temperature to about 80 ° G. While the proper energy level will vary as shown in the foregoing, this teaching provides a general guideline for any person skilled in the art to easily apply the appropriate energy level to be used in carrying out the present invention. the invention.

Once the particulate polyester prepolymer resin has been crystallized, dried and heated to solid phase polymerization temperatures, it is in a state in which it can be solid phase polymerized by known methods such as fluid bed type processes, ; fixed or so-called static bed, plug flow bed or gravity flow bed such as, for example, according to U.S. Patent No. 5,756,990 or discontinuous processes such as those using rotary mixer dryers. Preferably, the treated prepolymer resin will be discharged from the high frequency heater directly into polymerization reservoirs, which will such methods are used. However, the treated prepolymer resin; also are discharged into container reservoirs or bunkers for subsequent polymerization depending on the nature and design of the particular process employed.

In general, these processes will be conducted in such a way that the treated particulate polyester-20 prepolymer is heated to temperatures ranging from about 185 ° C to 250 ° C and more preferably between 210 ° C and 24 ° ° C and maintained within these temperature ranges in an inert gas stream or under reduced pressure until the desired molecule has achieved weight.

The invention has been illustrated in the preceding examples using polyethylene terephthalate since this particular ester is preferred in view of its importance and wide use as a base material in the manufacture of such products as, films and fibers and more recently carbonated drink -... 50 bottles. However, it will be apparent to one skilled in the art of polyesters that the invention is applicable to the simultaneous and continuous crystallization, drying, and heating of other particulate, melt-polymerized, low molecular weight polyester prepolymer resins intended to be under 55 throws of solid phase polymerization conditions. Representative examples of such other prepolymer resins include those resins prepared by melt polymerizing the reaction product of dicarboxylic acids or their alkyl esters, wherein the alkyl group contains from 1 to 4 carbon atoms with the polymethylene glycols containing from 2 to 40 carbon atoms.

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Claims (6)

A process for "preparing high molecular weight particulate polyesters having an intrinsic viscosity of at least 0.6 dl per g by solid phase polymerization of a corresponding low molecular weight particulate melt-polymerized linear condensation polyester prepolymer resin having an intrinsic viscosity of at least 0.35 dl per g, characterized in that simultaneously and continuously (a) the particulate prepolymer resin with an initial density of 1.34 g per cm or less crystallizes to a density range of about 1.37 to about 1.39 S per cm, (b) the particulate prepolymer having an initial water content of about 0.40% to about 0.25% dries to a water content ranging from about 0.10% to about 0.005% and (c) heating the particulate prepolymer to a solid phase polymerization temperature ranging from about 185 ° C to about 250 ° C by the particulate prepolymer subjecting the resin to a continuous and continuous field of high frequency energy in the range of about 20 MHz to about 300 MHz over a period of time ranging from about 20 seconds to about 90 seconds. 2. A method according to claim 1, characterized in that a continuous and continuous field of high frequency energy is applied in the range from about 25 MHz to about 150 MHz. 3. A method according to claim 2, characterized in that a high frequency energy field is used ranging from about 27 MHz to about 100 MHz. A process according to claim 1, characterized in that the particulate melt-polymerized linear condensation polyester prepolymer is heated in the field with high frequency energy to a solid phase polymerization temperature, which is from about 210 to about 240 ° C varies. Process according to claim 1, characterized in that alse-cellular, melt-polymerized linear condensation polyester prepolymer polyethylene terephthalate is used. 6. Process according to claim 1, characterized in that an initial temperature of the polyethylene terephthalate for 8100379 polymer is used, which varies from about ambient temperature to about 80 ° C. 8 1 0 0 37 9